The Divine Liturgy of St. Gregory the Great is one of the liturgies authorized for use by the AntiochianWestern Rite Vicariate (AWRV). It is authorized for use in the AWRV in two forms—that of the Orthodox Missal and that of the Saint Andrew's Service Book, although nearly all parishes in the AWRV celebrate only that of the Orthodox Missal. The basis of the liturgy is the ancient Roman Mass, though corrected to comply with Orthodox theology. It is also authorized for use within the Russian Orthodox Church Outside Russia (ROCOR). In the past, the Liturgy of St. Gregory has been celebrated by the Polish Orthodox Church, the Patriarchate of Moscow, and the Alexandrian Patriarchate.